1. Field of the Invention
The present invention relates to the field of measurements systems for electronic components and devices like power amplifiers and other. It also relates to methods for characterizing and analyzing the behavior of such devices.
2. State of the Art
Presently source-pull and load-pull techniques are used to characterize amplifiers under different impedance conditions and to find the optimal source and load matching circuitry for certain component characteristics. Source-pull provides different impedances at the input of the device while load-pull provides different impedances at the device output. Different device characteristics are measured under different impedance conditions in order to find the impedance condition that optimizes one or more characteristics. To provide different impedances to the amplifier, two main approaches exist: passive (mechanical or electrical) or active techniques (active loop or power injection from external source).
Because the tuning process is cumbersome (e.g., tuners and system parts need to be characterized separately) and the measurement process is slow, no real-time feedback is given. Therefore, the measurement set-ups are automated to collect power amplifier characteristics, while tuning the output and input impedance, while stepping power levels, etc. The calculated characteristics are displayed afterwards, typically using contour plots of these characteristics on a Smith chart.
For mechanical passive tuners, typically a step motor is used to control the tuning of the mechanical part (e.g., position and depth of a probe or resonance circuit dimensions), while for electrical passive tuners an electrical characteristic of a component is adapted to change the presented impedance (e.g., changing transmission line length using PIN diodes). For active tuners using an active loop, the amplifier output wave is sampled using a coupler structure, amplified/attenuated and phase shifted before injecting back towards the component under test. To avoid a feedback loop, the source at the input can be split towards the output via a gain/attenuation and phase control. As an alternative a second synthesizer is used at the output, locked to the synthesizer at the input. By controlling the amplitude and phase of the second source, different impedances are realized. These approaches to active injection are described in patent documents WO03/048791-A2 and U.S. Pat. No. 6,509,743-B as well as in the paper “A Time Domain Large Signal Measurement Setup” (H. Arthaber et al., Int'l Journal of RF and Microwave Computer-Aided Engineering, Vol. 15, No. 1, January 2005, pp. 3-12). In patent document U.S. Pat. No. 6,348,804-B1 the active approach with two separate sources is explained in the context of extracting scattering parameters faster and in more realistic conditions.
To measure the amplifier characteristics a first vector network analyzer is used off-line to characterize all parts of the measurement set-up (by their S-parameters), while during source-pull and load-pull a power meter is used to measure the transferred power (see FIG. 1). Disposing of the S-parameters of the different components in the set-up and measuring the transferred power, one can calculate a lot of important device characteristics but not all. For the above-mentioned active tuner systems, a vector network analyzer is usually required to measure each time the synthesized impedances.
With the prior art systems as shown in FIG. 1, source-pull is performed by changing the states of the source tuner, while maintaining the impedance at the output to a constant value and regulating the microwave synthesizer to maintain a given available power. This is repeated for different levels of available power, requiring the microwave (or RF) synthesizer to step through a range of values. The source tuner and the source match of the synthesizer need to be pre-characterized. During source-pull it is also assumed that the source match of the synthesizer does not change. With the prior art systems as shown in FIG. 1, load-pull is performed by changing the states of the load tuner, while maintaining the impedance at the input at a constant value and regulating also the microwave synthesizer to maintain a given available power. Of course, the combination of source-pull and load-pull is possible.
Set-ups (as explained in WO03/048791) based on oscilloscopes or Microwave Transition Analyzers (obsolete instrument from Agilent Technologies) have been constructed to characterize transistors, power amplifiers in time and frequency domain, while measuring voltages and currents at the input and output. These types of system can provide complete component information. The systems have been combined with passive tuners and active tuners.